Building Services and Finishes Factor - Multi-Storey Building Form.

In buildings requiring anything other than minimal electrical services distribution, the inter-relationship of the structure, the mechanical and electrical services and the building finishes will need to be considered together from the outset.

It is essential to co-ordinate the details of the building services, cladding and structure at an early stage of the project in order to produce a building which is simple to fabricate and quick to erect. Apparently minor variations to  the steelwork, brought about by services and finishes requirements defined after a steel fabrication contract has been let, can have a disproportionate effect on the progress of  fabrication and erection. Steel buildings impose a strict discipline on the designer in terms of the early production of final design information. If the designer fails to recognize this, the advantages of steel-framed building cannot be realized.

The integration of the building services with the structure is an important factor in the choice of an economic structural floor system. The overall depth of the floor construction will depend on the type and distribution of services in the ceiling void.

The designer may choose to separate the structural and services zones or accom- modate the services by integrating them with the structure, allowing for the structural system to occupy the full depth of the floor construction. (See Fig. 2.4.)


Building services and floor structure: (a) separation of services and structure; (b) integration of services and structure
Fig. 2.4 Building services and floor structure: (a) separation of services and structure; (b)
integration of services and structure

Separation of zones usually requires confining the ducts, pipes and cables to a horizontal plane below the structure, resulting in either a relatively deep overall floor construction or close column spacings. Integration of services with structure requires either deep perforated structural components or vertical zoning of the  services and structure.

For the range of structural grids used in conventional building, traditional steel floor construction is generally deeper than the equivalent reinforced concrete flat slab: the difference is generally 100–200mm for floor structures which utilize com- posite action and greater for non-composite floors (Fig. 2.5).The increased depth is only at the beam position; elsewhere, between beams, the depth is much less and the space between them may accommodate services, particularly if the beams may be penetrated (Fig. 2.6). The greater depth of steel construction does not therefore necessarily result in an increase in building height if the services are integrated within the zone occupied by the structure.A number of possible solutions exist for integrated systems, particularly in long-span structures utilizing castellated, cellular or stub-girder beams. (See Fig. 2.7.)


Overall floor depths: (a) R.C. flat slab; (b) composite; (c) non-composite
Fig. 2.5 Overall floor depths: (a) R.C. flat slab; (b) composite; (c) non-composite



Ceiling voids: (a) steel frame: variable void height; (b) concrete slab: constant void height
Fig. 2.6 Ceiling voids: (a) steel frame: variable void height; (b) concrete slab: constant void
height



 Integration of services
Fig. 2.7 Integration of services: (a) separated (traditional); (b) integrated (shallow floor
‘Slimdek®’ system); (c) integrated (long span ‘primary’ beam – stub girder); (d) inte-
grated (long span ‘secondary’ beams)



A number of solutions have been developed which allow long spans to co-exist with separation of the building services by profiling the steel beam to provide space for services, either at the support or in the span. Automated plate cutting and welding techniques are used to produce economical profiled plate girders, with or without web openings. (See Fig. 2.8.)

Tapered beams and services
Fig. 2.8 Tapered beams and services

Overall depth may be reduced by utilizing continuous or semi-continuous rather than simple connections at the ends of the beams. This reduces the maximum bending moment and deflection. However, such solutions are not as  efficient as would first appear since the non-composite section at the support is much less  efficient than the composite section at mid-span. Indeed, if the support bending moments are large in comparison with the span bending moments the depth  may be greater than the simply-supported composite beam. This is an expensive  fabrication in comparison with straight rolled beam sections. (See Fig. 2.9.)


Floor depth: (a) simple; (b) semi-continuous; (c) continuous
Fig. 2.9 Floor depth: (a) simple; (b) semi-continuous; (c) continuous

In addition, the use of continuous joints can increase column sizes considerably.

Semi-continuous braced frames can provide an economic balance between the primary benefits associated with simple or continuous design alternatives. The degree of continuity between the beams and columns can be chosen so that complex stiffening to the column is not required. Methods of analysis have been developed for non-composite construction to permit calculation by hand. It is possible to achieve reduced beam depths and reduced beam weights.

The overall depth may also be reduced by using higher-strength steel, but this is only of advantage where the element design is controlled by strength. The stiffness characteristics of both steels are the same: hence, where deflection or vibration govern, no advantage is gained by using the stronger steel.

Recently, shallow floor systems have been developed for spans up  to about 9m which allow integration of services within the slab depth. Structural systems range from conventional fabricated beams using precast units to proprietary systems using new asymmetric rolled beams and deep metal decking. These approaches can form the basis of energy-saving sustainable solutions.

Semi-continuous braced frames can provide an economic balance between the primary benefits associated with simple or continuous design alternatives. The degree of continuity between the beams and columns can be chosen so that complex stiffening to the column is not required. Methods of analysis have been developed for non-composite construction to permit calculation by hand. It is possible to achieve reduced beam depths and reduced beam weights.

The external skin of a multi-storey building is supported off the structural frame.

In most high quality commercial buildings the cost of external  cladding systems greatly exceeds the cost of the structure. This influences the design and construction of the structural system in a number of ways:

• The perimeter structure must provide a satisfactory platform to support the cladding system and be sufficiently rigid to limit deflections of the external wall.
• A reduction to the floor zone may significantly reduce the area and hence cost of cladding.
• Fixings to the structure should facilitate rapid erection of cladding panels.
• A reduction in the weight of cladding at the expense of cladding cost will not necessarily lead to a lower overall construction cost.

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